The invention relates to a communications process, to a transmitting device and to a receiving device.
In connection with transmitting devices it is desirable to optimize the minimum value of the transmitting amplitude, for example, on the basis of amplitude dependent distortions and the service life of the carrier source. This may mean that, with fixed transmission parameters, a minimum maximum value for the transmitting amplitude of the transmitted communications signal is desirable and care must be taken that the lowest possible minimum value of the signal amplitude does not fall below a threshold value that is specific for the carrier source.
U.S. Pat. No. 4,789,987 discloses an optical transmitter which automatically regulates the minimum value of the signal amplitude of the communications signal by way of a carrier source specific threshold value and at the same time keeps the maximum amplitude of the communications signal at a minimum. In the prior art signal source, which is a laser diode, a so-called clipping effect occurs if the threshold value is not reached and leads to a distortion in the communications signal.
If one now considers the probability distribution curve of the signal amplitudes which serve to modulate the carrier sources, one notes that one of the two ends of this distribution curve ends below the threshold value which leads to distortion in the communications signal. In order to reduce the probability of the amplitude falling below the threshold value, the prior art circuit increases the direct current component of the injection current. The result is that the maximum value as well as the mean value of the probability distribution curve of the transmission amplitudes increases.